1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method of fabricating the same. More particularly, the present invention relates to a liquid crystal display device and a method for fabricating the same having a common auxiliary electrode capable of preventing electric field dispersion, stabilizing the alignment of liquid crystal material, and wherein an aperture ratio of the LCD device is increased.
2. Discussion of the Related Art
Over time, demands on display technology have gradually increased and resulted in the development of a variety of flat display panels including liquid crystal displays (LCDs), plasma display panels (PDPs), electro luminescent displays (ELDs), vacuum fluorescent displays (VFDs), etc. Some of the aforementioned flat panel display panels are currently being employed as displays of various apparatuses.
Owing to their excellent picture display quality, light weight, thin dimensions, and low power consumption, LCDs are being developed for use as televisions (TVs), capable of receiving and displaying broadcasted signals, and are widely used in portable displays as monitors of notebook computers and the like.
Despite various technical developments in the LCD technology, however, research in enhancing picture quality of LCD devices has been lacking in some respects compared to research in other features and advantages of LCD devices. Therefore, to increase the use of LCD devices as displays in various fields of application, LCD devices capable of expressing high quality images (e.g., images having a high resolution and a high luminance) with large-sized screens, while still maintaining a light weight, minimal dimensions, and low power consumption must be developed.
LCDs generally include a liquid crystal display panel for displaying a picture and a driving part for providing driving signals to the liquid crystal display panel. The LCD panel generally includes first and second glass substrates bonded to each other and spaced apart from each other by a cell gap. A layer of liquid crystal material is injected into the gap between the first and second glass substrates. Light transmittance characteristics of the liquid crystal material may be selectively altered by electric fields generated between the first and second glass substrates to display images on the LCD panel.
Molecules of liquid crystal material contained between upper and lower substrates of Twisted Nematic (TN) mode LCDs are aligned along longitudinal directions substantially parallel with the lower and upper substrates and are generally spirally twisted to a predetermined pitch such that the alignment of the longitudinal directions within the liquid crystal molecules is continuously changeable.
The light transmittance characteristics of TN mode LCDs generally varies across each gray level in accordance with a corresponding viewing angle. Further, TN mode LCDs distribute light symmetrically in right and left directions while distributing light asymmetrically in lower and upper directions. Accordingly, gray inversion of images is generated.
Use of Vertical Alignment (VA) mode LCDs has been proposed to overcome the aforementioned problems and compensate for variations in light transmittance characteristics across viewing angles. In VA mode LCDs, a pixel region is divided into a plurality of domains, wherein liquid crystal material aligned in different directions in each of the domains. In VA mode LCDs either a protrusion or an electric field inducing window is formed on the upper substrate while a common auxiliary electrode (i.e., side electrode) is formed on the lower substrate.
A related art LCD device will now be explained in greater detail below.
FIG. 1 illustrates a schematic view of a related art LCD device and FIG. 2 illustrates a cross-sectional view of the related art LCD device shown in FIG. 1 taken along line I-I′.
A related art LCD device generally includes opposing lower and upper substrates 1 and 10 and a layer of liquid crystal material 16 interposed between the lower and upper substrates 1 and 10.
The lower substrate 1 includes a plurality of gate lines 2 and data lines 4 crossing each other, pixel regions defined at each of the crossings of the gate and data lines 2 and 4, a gate electrode (not shown) extending to both sides of the gate line 2, a gate insulating layer (not shown) formed over the lower substrate 1 and on the gate line 2, an active region 3 formed over the gate insulating layer in a region above the gate line 2, a pixel electrode 7 formed within the pixel region and formed out of the same layer as that of the active region 3, a source electrode 4a extending from the data line 4 and overlapping a first portion of the active region 3, a drain electrode 4b formed apart from the source electrode 4a and overlapping a second portion of the active region 3 as well as a predetermined portion of the pixel region 7, an interlayer passivation film 6 formed over an entire surface of the lower substrate 1 and on the pixel electrode 7, an orientation control electrode 5 formed over the interlayer passivation film 6 and overlapping the circumference of the pixel electrode 7, and a first alignment layer 8 formed over the lower substrate 1 and on the orientation control electrode 5. Orientation control electrodes 5 of adjacent pixel regions are connected to each other.
The upper substrate 10 includes a black matrix layer (not shown) for preventing light leakage in regions outside the pixel regions of the lower substrate 1, a color filter layer (not shown) formed in regions over the upper substrate 10 corresponding to the black matrix layer and the pixel regions of the lower substrate 1, a common electrode 13 formed over the color filter layer wherein the common electrode 13 has an “X”-shaped orientation control window 14, and a second alignment layer 15 formed over the upper substrate 10 and on the common electrode 13.
Referring to FIG. 2, when an electric field is generated between the pixel electrode 7 and the common electrode 13, a fringe field (designated by the solid arrows) is generated by the orientation control window 14 within the common electrode 13. Affected by the fringe field, liquid crystal molecules become aligned differently at opposing sides of the orientation control window 14 and, accordingly, compensate for variations in light transmittance characteristics across viewing angles.
Use of LCD devices such as those illustrated in FIGS. 1 and 2 is disadvantageous for the following reasons. For example, the orientation control electrode 5 is formed of an opaque metal and is spaced apart from the data line 4 by a predetermined distance to prevent the generation of an electrical short. Because the orientation control electrode 5 is spaced apart from the data line 4, a width of the pixel region decreases thereby decreasing aperture ratio and luminance of the LCD device. To compensate, the related art LCD devices illustrated in FIGS. 1 and 2 require backlights of increased brightness and therefore require an increased level of power consumption.
Moreover, electrical fields generated in TN mode LCD devices face outwardly toward the perimeter of the pixel. Accordingly, alignment of the liquid crystal material becomes unstable and light leakage is generated at the perimeter of each pixel region, decreasing the overall brightness of the LCD device. Furthermore, alignment of the liquid crystal material becomes unstable when a light force is applied the LCD panel and a spot is generated that is difficult to remove due to a slow response time of the liquid crystal material.